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Hello Siegfried,
This is a wonderful dial. The construction of this moon dial is given by
Jacques Ozanam in 1693 in his "Cursus Mathematicus: or A Complelat Course of
the Mathematicks." Vol V Part III, "A Treatise of Gnomonicks", Problem XX.
This work is available from the NASS website Shadow Catchers series.
To read the dial you must know the age of the moon, or number of days since the
last new moon. The lunar age is given next to the meridian (noon) line with
1-15 on the left side and 16-29 on the right side. These numbers apply to the
lines perpendicular to the meridian. Find the line for the current lunar age
and locate where the moon's shadow intersects this lunar age line. There will
be a slanted or curved line close to the intersection. This is the local solar
time line. Follow the curved line the the edge of the dial to read the local
solar time from the moon's shadow.
Hope this helps,Mark
On Monday, July 10, 2023 at 06:17:46 AM CDT, siegfried.netzb...@t-online.de
<siegfried.netzb...@t-online.de> wrote:
Dear sundial friends,
came across an interesting moon dial which is quite different from all the
other moon dials I did see up to now
(https://kabinett.mapublishing-lab.uni-koeln.de/objekte/monduhr). However: I
cannot read it, neither do I understand the way they calculated the lines on
the dial to (may be) read off the time.
The dial does not have the usual numeric list where you can determine the age
of the moon with the aid of the size of the illuminated moon. The age of the
moon, i.e. the angle between moon and sun is needed to determine time using the
moon shadow on a sun dial at night.
How do you read this dial and what is the basis (theory) for the lines to read
of the time on this dial? Is there someone who can help? I would be very
thankful for any help or advice.
Thank You for Your help!
Regards
Siegfried Netzband
Siegfried Netzband
Hebelstr. 12
75233 Tiefenbronn
Tel: 07234 2802
Fax: 07234 942909
Mob: 0151 53083636 / 0160 1531634
E-Mail: siegfried.netzb...@t-online.de
Skype: siegfried75233
www.ferienhaus-frieseneck.de
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